During cataract surgery, the cataract is removed and an intraocular lens (IOL) may be implanted in the eye of a subject to replace the natural crystalline lens. The natural lens must first be removed, for instance, using a phacoemulsification system. The IOL is then generally implanted using an insertion apparatus or device that rolls, folds, or otherwise configures the lens for delivery through a small incision in the eye in a way that reduces trauma and expedites post-surgery healing.
The IOL is stored separately and transferred to an injector or cartridge just prior to delivery. Typically, the injector or cartridge is first partially filled with a liquid or gel, for example, a viscoelastic lubricating agent or “Ophthalmic Viscosurgical Device” (OVD). The lubricating agent facilitates passage of the IOL through the injector. The surgeon also injects some of the lubricating agent directly into the eye to facilitate insertion and positioning of the IOL. One family of viscoelastic substances used is sodium hyaluronate sold under the trade name Healon®, though Balanced Salt Solutions (BSS) and other lubricating agents are used.
Viscoelastic lubricating agents are commonly sold pre-filled in a syringe provided with a thin cannula tip. Glass syringes are used to avoid any degradation of the syringe and lubricating agent during storage. A syringe is typically gripped by the thumb and fingers in one hand and is used by depressing the plunger rod with the thumb axially along the syringe axis with the fingers holding a flange at the rear end of the syringe barrel. Due to manufacturing constraints with glass syringes, the flange at the rear end of the syringe barrel is relatively small and annular. Because of the thin cannula tip and viscoelastic nature of the lubricating agent, a relatively large squeezing force may be required and the small annular flange presents an ergonomic hindrance. Consequently, press-on finger grips are typically provided with the pre-filled syringe which snap onto the annular flange and greatly increase the surface area available.
U.S. Pat. No. 5,700,247 to Becton Dickinson France S.A. discloses a backstop device for a so-called flangeless syringe (which nonetheless has a small flange), which serves to provide a large finger grip. The backstop device has an opening that describes a partial circle which can be snapped over the cylindrical syringe barrel flange. Currently, Becton Dickinson markets a glass HYPAK syringe that is sold with a similar backstop device. Although the backstop device for the HYPAK syringe improves functionality by providing a large finger grip, it is only retained on the syringe by friction in a snap-fit arrangement, much like several other commercial finger grips. If a user places a rotational or horizontal force on the plunger relative to the finger grip, these devices can suddenly become disconnected from the syringe body. This can be extremely dangerous if the user is in the process of injecting lubricant into the eye.
It would be advantageous to provide a finger grip for syringes which avoids these disadvantages.